1. Field of the Invention
The present invention relates to an automatic marking device for a lensmeter which is used for measuring the refractive characteristics of spectacle lenses.
2. Description of the Prior Arts
A lensmeter generally has two major functions, namely, a measuring function for measuring the refractive characteristics, such as spherical refractive index, cylindrical refractive index, axis angle and prism refractive index of a lens, and a marking function for marking the optical center and the cylindrical axis in the unedged lens as the references for edging the lens to have the same fitted to a spectacle frame.
In recent years, automatic lensmeters capable of automatically measuring the refractive characteristics have been put into the practical use. These automatic lensmeters, however, are not able to conduct the marking automatically and the marking has to be done manually even in these automatic lensmeters.
The difficulty encountered in the manual marking operation is attributable to the fact that this operation includes two kinds of work, namely, aligning and marking. The aligning work is the work for attaining optical alignment between the optical center of the lens or the optical point of action with the measuring axis of the lensmeter. Any misalignment will lead to an error in the measured values of refractive indexes. Since the making stylus of a lensmeter is adapted to be moved to a position on the measuring axis and to effect the marking at this position, so that any misalignment directly causes an error in the marking position.
In the marking operation, when the lens has a cylindrical refracting power, the direction of the cylinder axis is marked by means of three marking means arranged on a line. Since the groups of the marking stylus are not rotatable, it is necessary that the lens itself is rotated for the purpose of marking of the cylinder axis direction. The rotation of the lens also is one of the factors which cause the error.
Thus, the conventional marking operation often causes errors in the measurement of the refractive characteristics and in the marking position due to its complexed nature, and requires a long working time. Therefore, although the known automatic lensmeter permits an automatic high-speed measurement of the refractive characteristics, such automatic lensmeter cannot provide any substantial shortening of the whole measuring time including the alignment and marking over the conventional manual lensmeter.